Position location solutions typically implement a receiver on the mobile device for which the location is to be determined. The receiver on the mobile device receives signals transmitted from known stationary points (e.g. geosynchronous satellites, terrestrial wireless base stations). The characteristics of the signals received at the mobile device (i.e. time of arrival, signal strength) are used to determine the location of the mobile device relative to the stationary transmitter locations. The location of the mobile device is determined is by calculating the distance of the device from each of the known stationary transmitters and then, with a previously known relationship between the stationary transmitters, using triangulation to isolate the position of the mobile receiver.
Stationary transmitters implemented in the form of geosynchronous satellites have the advantage of providing a very large coverage area, however, the low-power signal employed and the ever-changing contour and center of gravity of the earth requires continuous correction of reference distances between satellites and a sophisticated receiver on the mobile device. In addition to the sophisticated receiver requirements, the satellite signals are difficult to receive within buildings making it challenging to provide accurate location determinations when not outdoors. The difficulty of receiving satellite signals inside building is compounded by limitation of the resolution of position location using satellite positioning which is typically in the 3 to 10 meter range at best indoors.
For indoor applications, the low accuracy resolution makes it difficult to distinguish the location between adjacent rooms and floor levels in the facility. A 10-meter resolution, for example, might only isolate the mobile device location to one of any of six adjacent rooms each on one of three floors within a multi-story multi-room facility such as a patient ward in a hospital.
Terrestrial wireless transmitters such as wireless local area network access points (WLAN AP) and wireless wide area network base stations (WWAN BS) have been used for implementing the stationary transmitters for position location. These have the advantage of being compatible with relatively simple receivers in the mobile devices when compared to the geosynchronous satellite implementation alternatives and also have the benefit of providing data and voice communications services in addition to location. The disadvantage of WLAN AP and WWAN BS stationary transmitter-based position location systems is that the resolution accuracy is equal to or less than that of the geosynchronous satellite solutions making indoor applications difficult to implement.
A key inhibitor of the WLAN AP and WWAN BS transmitter-based position location systems is the use of signal strength as the primary determination of the distance from an individual stationary transmitter to the mobile receiver. Because of multi-path transmission and shadowing issues, the use of received signal strength to calculate distance results in, at best, 3 meter accuracy of these solutions and, consequently, in the same ambiguous mobile receiver location determination and restricted marketable applications of these types of solutions.
Significant improvements in the sophistication of WLAN AP and/or WWAN BS solutions for Local Positioning would need to be made coupled with advancements in the mobile device sophistication to provide a power-efficient, low-cost Local Positioning Solution that delivers location resolution fine enough to achieve room-by-room level location within a facility.